Diagnostic Criteria for Dementia

May 25, 2021

Diagnostic Criteria for Dementia

Diagnostic Criteria for Dementia

Posted in : Diagnosis on by : Catherine Verner

Have you or your loved one noticed changes that affect daily life and want to find out if the reason is dementia or something else? This article outlines the diagnostic criteria for dementia and how doctors approach, assess and investigate a dementia diagnosis. 

A diagnosis of dementia does not come from just one specific test, but is based on several different factors, including changes in memory, planning, judgment, decision-making, social skills, and day-to-day function.  Changes in mood and personality can also be common, such as increased anxiety, suspicion and fearfulness.

Visiting a Doctor

The doctor (which you might refer to as a GP, family doctor or primary physician depending on the country you reside in) will carry out an initial investigation and will consider a number of factors. This may include: 

  • Current Symptoms & Medications
  • Past Medical History
  • Physical Examination
  • Cognitive Assessment
  • Blood Tests
  • Urine Test
  • Brain Scans

It is recommended that you bring along someone who knows you well to help describe any changes that they may have noticed. https://cognihealth.in/blog/diagnosis/what-to-expect-when-being-diagnosedAt this appointment, the doctor will ask about the changes you have been experiencing, when they started, and their impact on your daily life.  They will also ask about any current or past conditions such as a stroke, heart disease, or diabetes and associated medications being taken. Understanding this will help them rule out other reasons for similar symptoms, including possible side effects from any new medications. To better understand what to expect during this type of appointment and how you can prepare for it, check out What to expect when being assessed

Cognitive Assessment (Mental Ability Tests)

The doctor may want to carry out a cognitive assessment to assess different brain functionalities. A number of different tests can be used, such as Mini Mental State Examination (MMSE) or the General Practitioner Assessment of Cognition (GPCOG). While these tests cannot give a definitive diagnosis of dementia, they will help assess several different mental abilities such as short and long-term memory, concentration and attention, and awareness of time and place. 

The test will provide a score that can help the doctor decide if further investigation is needed. The maximum score possible on the MMSE test is 30 points. The MMSE score denotes the severity of cognitive impairment as follows:

  • Mild: 21–26,
  • Moderate: 10–20,
  • Moderately severe: 10–14,
  • Severe: less than 10.

While a high score indicates stronger mental abilities, receiving a high score may not necessarily mean a person does not have dementia, and a low score does not imply a person does have dementia. This is why an overall health assessment is considered. At this stage, the doctor is merely gathering information  to try to pull together a picture of what may or may not be going on.

Blood Tests

Your doctor may also arrange for blood tests to be carried out. This will help exclude other causes of symptoms such as problems with thyroid, kidney, liver function, and diabetes.  The doctor may also check for Vitamin B12 and folate deficiencies. 

Urine Test

A urine test will help rule out any infection, which can also cause confusion, agitation, and changes in behaviour in older and more frail people.

If the doctor feels that further investigation is required, a referral will be made to a specialist such as a psychiatrist at a local hospital or a memory clinic.

Brain Scans

Not everyone will be given a brain scan. However, a specialist may use this as part of the overall assessment and to rule out other conditions with similar symptoms such as a brain tumour, head injury or stroke.  

MRI (Magnetic Resonance Imaging) Scan

An MRI scan may be recommended, which can help confirm a diagnosis and also provide information on the type of dementia.  For example, this type of scan can show:

  • Reduced blood flow to the brain, caused by narrowing and blockage of small blood vessels inside the brain which can happen as a result of a stroke. These changes are often associated with Vascular dementia.  
  • Changes in frontal and temporal lobes are related to Frontotemporal dementia.
  • Changes in the temporal lobe and lesions in the hippocampus are associated with Alzheimer’s disease.

It might be helpful to watch the following video which outlines the experience of a person getting an MRI and explains how MRI scans can help better understand what is happening in one’s brain:

CT (Computerised tomography) scan

A CT scan may be organised. This type of scan uses x-rays to detect any changes in brain structure, change to blood vessels, and detect strokes. During a CT scan, you will be asked to lie on your back on a table over which there is a machine that scans your brain, which can take around 20 minutes. 


There are several other types of brain scans as well that  provide insight into the brain as it functions. These scans are called functional brain imaging and include functional MRI (fMRI), single-photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetoencephalography (MEG). 

  • fMRI uses radio waves and a strong magnetic field to measure the metabolic changes in active parts of the brain. 
  • SPECT shows the distribution of blood in the brain. 
  • PET scans can detect changes in glucose metabolism, the presence of amyloid proteins, tau protein, oxygen metabolism, and blood flow.

Diagnosis Time Frame

The timeframe from initially suspecting symptoms to receiving a diagnosis can vary enormously. Many people delay going to the doctor as they believe the symptoms are related to normal ageing. However, once scans and tests have been carried out, a timeframe for diagnosis has been estimated at between 4 and 12 weeks. 

Further information on the NICE clinical guidance used by healthcare professionals in diagnosing dementia can be found here.


NHS: Tests for Diagnosing Dementia 

NICE: Health Technology Appraisal

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